A father and son have been shot in an inner-city Sydney street. Police believe the shooting was a targeted attack and say the victims were known to them.

Witnesses heard up to eight shots on Sunday night before finding a 49-year-old man, understood to be Michael Smart, lying in Jones Street in Pyrmont in a pool of blood with a gunshot wound to his head. His 23-year-old son Josh, an aspiring boxer, was shot in the back.

Residents said they had not heard any arguing or screaming before the shots were fired.

Ashlie Lomas came out on to the street to find Michael Smart on the ground. "We came out the front and that is when we saw everyone screaming and running around," she said.

Lomas said she and other witnesses had given first aid and used towels to stop his bleeding. "We were just trying to get him to hold on," she said. "By the end of it the family calmed down and he started to breathe a lot better."

Michael Smart is in hospital in a critical condition while Josh Smart is in a stable condition.

On Monday morning the street was cordoned off as detectives combed the footpath looking for evidence. Blood-soaked towels were strewn on the footpath.

Police believe one shooter was involved. Detective Inspector John Maricic said he did not believe the attack was linked to several other recent Sydney shootings. There also did not appear to be any gang links.

"It's too early in the investigation stage to determine what the cause of it was," he said.